In a laterally diode-pumped, solid-state laser, such as a laser having a resonator including a neodymium-doped yttrium aluminum garnet (Nd:YAG) gain-medium, laser pump-power can be raised to a level at which thermally induced birefringence in the Nd:YAG gain-medium can cause fundamental-wavelength radiation circulating in the resonator to be unpolarized. The radiation can not be caused to be polarized without considerable loss of efficiency of generating the radiation.
Unpolarized fundamental-wavelength radiation can be frequency-doubled in an optically nonlinear crystal, as the crystal can resolve from the unpolarized radiation a portion thereof that is polarized in an orientation for which the crystal is cut. Intracavity frequency-tripling, however, involves a frequency-doubling step in a first optically nonlinear crystal and a sum-frequency mixing step (in which fundamental-wavelength radiation is mixed with the frequency-doubled radiation) in a second optically nonlinear crystal. This is about 50% less efficient with unpolarized fundamental-wavelength radiation, as the fundamental-wavelength radiation and the frequency-doubled radiation entering the crystal must both be polarized on entering the second crystal, with the polarization planes being either the same or perpendicular to each other, depending on whether the sum-frequency mixing is of type-I or type-II, respectively.
There is a need for a high-power solid-state laser-resonator arrangement in which polarized radiation can be generated efficiently at high power even in the presence of strong thermal birefringence in the gain-medium. The resonator arrangement should be adaptable for efficient intracavity frequency-conversion in one or more optically nonlinear crystals.